linux-kernel - Re: [PATCH v3 2/2] PCI: imx6: Add IOMMU and ITS MSI support for i.MX95

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Message-ID: <20241103062305.6cqftpv4bwneg2mo@thinkpad>
Date: Sun, 3 Nov 2024 11:53:05 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Frank Li <Frank.li@....com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev, alyssa@...enzweig.io, bpf@...r.kernel.org,
	broonie@...nel.org, jgg@...pe.ca, joro@...tes.org,
	lgirdwood@...il.com, maz@...nel.org, p.zabel@...gutronix.de,
	robin.murphy@....com, will@...nel.org
Subject: Re: [PATCH v3 2/2] PCI: imx6: Add IOMMU and ITS MSI support for
 i.MX95

On Sat, Nov 02, 2024 at 01:26:46PM -0400, Frank Li wrote:

[...]

> > > +
> > > +	target = NULL;
> > > +	err_i = of_map_id(dev->of_node, rid, "iommu-map", "iommu-map-mask", &target, &sid_i);
> > > +	target = NULL;
> >
> > What is the point in passing 'target' here?
> 
> See https://lore.kernel.org/imx/b479cad6-e0c5-48fb-bb8f-a70f7582cfd5@arm.com/
> Marc Zyngier's comments:
> 
> "Perhaps it is reasonable to assume that i.MX95 will never have SMMU/ITS
> mappings for low-numbered devices on bus 0, but in general this isn't
> very robust, and either way it's certainly not all that clear at first
> glance what assmuption is actually being made here. If it's significant
> whether a mapping actually exists or not for the given ID then you
> should really use the "target" argument of of_map_id() to determine that."
> 
> See v4 https://lore.kernel.org/imx/20241101-imx95_lut-v4-2-0fdf9a2fe754@nxp.com/
> 

Okay, thanks! I was confused by the fact that you never used 'target' in this
version. But v4 clears it up.

- Mani

> +	target = NULL;
> +	err_m = of_map_id(dev->of_node, rid, "msi-map", "msi-map-mask", &target, &sid_m);
> +
> +	/*
> +	 * Return failure if msi-map exist and no entry for rid because dwc common
> +	 * driver will skip setting up built-in MSI controller if msi-map existed.
> +	 *
> +	 *   err_m      target
> +	 *	0	NULL		Return failure, function not work.
> +	 *      !0      NULL		msi-map not exist, use built-in MSI.
> +	 *	0	!NULL		Find one entry.
> +	 *	!0	!NULL		Invalidate case.
> +	 */
> 
> 
> >
> > > +	err_m = of_map_id(dev->of_node, rid, "msi-map", "msi-map-mask", &target, &sid_m);
> > > +
> > > +
> > > +	/*
> > > +	 * msi-map        iommu-map
> > > +	 *   Y                Y            ITS + SMMU, require the same sid
> > > +	 *   Y                N            ITS
> > > +	 *   N                Y            DWC MSI Ctrl + SMMU
> > > +	 *   N                N            DWC MSI Ctrl
> > > +	 */
> > > +	if (!err_i && !err_m)
> > > +		if ((sid_i & IMX95_SID_MASK) != (sid_m & IMX95_SID_MASK)) {
> > > +			dev_err(dev, "its and iommu stream id miss match, please check dts file\n");
> >
> > "iommu-map and msi-map entries mismatch!"
> >
> > - Mani
> >
> > --
> > மணிவண்ணன் சதாசிவம்

-- 
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